Process for xylene isomerization using ZSM-23 zeolite

Abstract

An improved process is disclosed for the isomerization of xylenes over a zeolite which may contain a platinum group metal. The improvement resides in the use of ZSM-23 zeolite which exhibits enhanced selectivity which inhibits the production of undesired C9+ aromatic transalkylation by-products. ZSM-23 having pores substantially unobstructed by silica, such as that made from a forming mixture containing amorphous precipitated silica as a silica source, has been found to be particularly useful in the process of the present invention.

What is claimed is: 
     
       1. A process for isomerizing an isomerization feed containing an aromatic C 8  mixture of ethylbenzene and xylene by which ethylbenzene and m-xylene conversion is enhanced, said process comprising contacting said feed under conversion conditions with a catalyst comprising ZSM-23 zeolite having a silica to alumina ratio of at least about 12, which zeolite is capable of sorbing greater than about 3 weight percent cyclohexane and greater than about 6.1 weight percent n-hexane. 
     
     
       2. A process for isomerizing an isomerization feed containing an aromatic C 8  mixture of ethylbenzene and xylene by which ethylbenzene and m-xylene conversion is enhanced, said process comprising contacting said feed, under conversion conditions with a catalyst comprising ZSM-23 zeolite having a silica to alumina ratio of at least about 12, capable of sorbing greater than about 3 weight percent cyclohexane and greater than about 6.1 weight percent n-hexane, which zeolite is prepared from a forming mixture containing amorphous precipitated silica as a silica source. 
     
     
       3. The process of claim 2 wherein said zeolite contains a Group VIII metal. 
     
     
       4. The process of claim 3 wherein said Group VIII metal is platinum. 
     
     
       5. The process of claim 2 wherein said zeolite is capable of sorbing greater than about 3.5 weight percent cyclohexane and 6.5 weight percent n-hexane. 
     
     
       6. The process of claim 2 wherein said conversion conditions include a temperature of from about 260° C. to about 538° C., a pressure of about 0 to about 1500 psig and a weight hourly space velocity of between about 0.5 and about 100. 
     
     
       7. The process of claim 2 wherein said aromatic C 8  mixture contains ethylbenzene, para-xylene, meta-xylene, and ortho-xylene. 
     
     
       8. The process of claim 2 wherein said zeolite is ZSM-23 predominately in the hydrogen form. 
     
     
       9. The process of claim 1 wherein said zeolite can sorb n-hexane and cyclohexane at a sorption ratio greater than about 1.5 weight percent n-hexane sorbed/weight percent cyclohexane sorbed at 40 mm partial pressure and room temperature. 
     
     
       10. The process of claim 9 wherein said sorption ratio is greater than about 2. 
     
     
       11. The process of claim 9 wherein said sorption ratio ranges between about 2 and about 4. 
     
     
       12. The process of claim 2 wherein said zeolite can sorb n-hexane and cyclohexane in a sorption ratio greater than about 1.5 weight percent n-hexane sorbed/weight percent cyclohexane sorbed at 40 mm partial pressure and room temperature. 
     
     
       13. The process of claim 12 wherein said sorption ratio is greater than about 2. 
     
     
       14. The process of claim 12 wherein said sorption ratio ranges between about 2 and about 4.